Butterfly valves are valves which can be used for isolating or regulating fluid flow through a pipe, passageway or plenum. The closing mechanism is in the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve designs. The disc is positioned in the center of the pipe or plenum. A rod passes through the disc and is connected to an actuator. The actuator turns the disc either parallel (open) or perpendicular (closed) to the flow. Unlike a ball valve, the disc is always present within the flow, therefore a pressure drop is always induced in the flow, regardless of valve position. A butterfly valve may also be opened incrementally to throttle flow.
Exhaust gas recycling (“EGR”) equipment directs exhaust gas flowing through an exhaust pipe of an engine for mixing with intake air flowing through an intake pipe to burn particulates trapped in a diesel filter. Other toxic substance in the exhaust gas may be combusted as well. EGR is used to reduce NOX emission produced in the combustion process. However too much EGR will cause the engine performance to suffer. Therefore the EGR must be precisely regulated.
Butterfly-type exhaust gas control valves for adjusting the EGR are known. Typically, the butterfly valve operates by a torque motor or actuator through a valve shaft. However, precise control of the exhaust gas flow is limited, especially when a low flow rate is desired. Currently available butterfly valves normally operate best in fully open or fully closed positions. Thus, a need exists for an improved butterfly-type valve or improved alternatives that provide improved flow control.